Mobility management processing method and apparatus

ABSTRACT

A mobility management processing method and apparatus are disclosed. The method includes: receiving, by an SMF network element, a data notification message that includes a PDU session identifier and that is sent by a UPF network element, and determining, based on the PDU session identifier, a session and SSC mode corresponding to the PDU session identifier and/or a service area of the UPF network element, where the UPF network element is a network element that establishes a PDU session corresponding to the PDU session identifier; determining a paging area based on the SSC mode and/or the service area of the UPF network element; and sending a first message including the paging area to an AMF network element, where the first message is used to trigger the AMF network element to page, in the paging area, a terminal that establishes the PDU session by using the UPF network element.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application a continuation of U.S. patent application Ser. No.16/578,011, filed on Sep. 20, 2019, which is a continuation ofInternational Application No. PCT/CN2017/077597, filed on Mar. 21, 2017.The disclosures of each of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the field of communications technologies,and in particular, to a mobility management processing method andapparatus.

BACKGROUND

In a next-generation wireless communications system, for example, in anew radio (New Radio, NR) system, a terminal establishes a protocol dataunit (Protocol Data Unit, PDU) session with a data network (DataNetwork, DN) network element by using a user plane function (User PlaneFunction, UPF) network element, and the PDU session provides a PDUconnection service between the terminal and the DN network element.

The PDU session has three session and service continuity (Session andService Continuity, SSC) modes (Mode): an SSC mode 1, an SSC mode 2, andan SSC mode 3.

SSC mode 1: In this mode, after the terminal establishes the PDUsession, regardless of any area to which the terminal moves or anyaccess technology, the UPF network element of the PDU session is used asan anchor to serve the terminal, that is, the PDU session is notinterrupted due to movement of the terminal.

SSC mode 2: In this mode, after the terminal establishes the PDUsession, if the terminal moves out of a service area of the UPF networkelement, a network may reselect a UPF network element for the PDUsession of the terminal, to trigger the PDU session served by theoriginal UPF network element and enable the terminal to establish a PDUsession after the UPF network element is reselected. In this mode, itmay be considered that the UPF network element has a specific servicearea. When the terminal moves within the service area, the UPF networkelement serves the terminal. However, if the terminal leaves the servicearea, a network side may determine that the UPF network element cannotserve the terminal, and the original PDU session established by usingthe UPF network element is interrupted.

SSC mode 3: In this mode, after the terminal establishes the PDUsession, the UPF network element also has a specific service area. Whenthe terminal leaves the service area of the UPF network element, anetwork selects a new UPF network element to serve the terminal, and theterminal establishes a PDU session with an original DN network elementby using the new UPF network element. However, a difference from the SSCmode 2 lies in that, a connection for the PDU session established by theterminal by using the previous UPF network element may not be releaseduntil establishment of a new PDU session is completed.

After the terminal establishes the PDU session and is in an idle state,when the UPF network element receives a downlink data packet from theterminal or a core network device such as the UPF network elementtriggers a control signaling process, the network side first needs topage the terminal within a range of a tracking area list (Tracking AreaList, TA List). Paging is performed on a per PDU session basis. To bespecific, the terminal is paged based on a PDU session to which thedownlink data packet or control signaling belongs, so that the terminalestablishes a connection to the network side for the PDU session.However, in some modes, for example, in the SSC mode 2, the terminal maynot be located in the service area of the UPF network element. If theterminal is not within the service area of the UPF network element,according to features of the SSC mode 2, a UPF network element of thePDU session may be reselected, causing the PDU session to be released.Therefore, in this case, the terminal cannot be precisely paged in theTA list range, and paging efficiency is reduced.

SUMMARY

This application provides a mobility management processing method andapparatus, to effectively perform mobility management on a terminal, sothat the terminal can quickly access a network.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

receiving, by a session management function SMF network element, a datanotification message that includes a protocol data unit PDU sessionidentifier and that is sent by a user plane function UPF networkelement, and determining, based on the PDU session identifier, a sessionand service continuity SSC mode corresponding to the PDU sessionidentifier and/or a service area of the user plane function UPF networkelement, where the UPF network element is a network element thatestablishes a PDU session corresponding to the PDU session identifier;

determining, by the SMF network element, a paging area based on the SSCmode and/or the service area of the UPF network element; and sending, bythe SMF network element, a first message including the paging area to anaccess and mobility management function AMF network element, where thefirst message is used to trigger the AMF network element to page, in thepaging area, a terminal that establishes the PDU session by using theUPF network element.

According to the method provided in this embodiment of this application,after receiving the PDU session identifier sent by the UPF networkelement, the SMF network element may determine, based on the PDU sessionidentifier, the SSC mode corresponding to the PDU session identifierand/or the service area of the UPF network element, so as to determinethe paging area for paging the terminal and instruct the AMF networkelement to page the terminal based on the paging area. The determinedpaging area is smaller than or equal to an area indicated by a trackingarea list of the terminal corresponding to the PDU session, so thatwhether the terminal can be successfully paged can be more quicklydetermined, thereby improving access efficiency of the terminal.

Optionally, the determining, by the SMF network element, a paging areabased on the SSC mode and/or the service area of the UPF network elementincludes:

if it is determined that the SSC mode is an SSC mode 2, using, by theSMF network element, the service area as the paging area; or

if it is determined that the SSC mode is an SSC mode 1 or an SSC mode 3,using, by the SMF network element as the paging area, an area indicatedby a tracking area list; or

determining, by the SMF network element, the paging area based on thetracking area list and the service area of the UPF network element.

Optionally, the determining, by the SMF network element, the paging areabased on the tracking area list and the service area of the UPF networkelement includes:

determining, by the SMF network element as the paging area, anoverlapping area of the service area and the area indicated by thetracking area list.

Optionally, the first message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times indicatesa quantity of times for which the AMF network element pages theterminal;

a paging cycle, where the paging cycle indicates a cycle in which theAMF network element pages the terminal; and

paging indication information, where the paging indication informationindicates a manner in which the AMF network element pages the terminal.

Optionally, the paging indication information indicates that if nopaging response is received in the paging area, the AMF network elementpages the terminal in the area indicated by the tracking area list.

Optionally, the method further includes:

starting, by the SMF network element, a first timer; and

if it is determined after the first timer times out that the AMF networkelement receives no paging response, sending, by the SMF networkelement, packet discard indication information to the UPF networkelement, where the packet discard indication information is used toinstruct the UPF network element to discard downlink data received fromthe terminal.

In the foregoing method, if it is determined after the first timer timesout that the AMF network element receives no paging response from theterminal, the SMF network element instructs the UPF network element todiscard downlink data packets received from the terminal. Especially fora PDU session in the SSC mode 2, if the terminal leaves the service areaof the UPF network element, a UPF network element needs to be reselectedfor the PDU session, and an IP address of the terminal device may needto change. Consequently, the PDU session may be interrupted, and thedata packets may no longer be sent to the terminal. Therefore, the datapackets may be discarded, so that network resources of the UPF networkelement can be saved, and system operation efficiency can be improved.

Based on a same inventive concept, an embodiment of this applicationprovides a mobility management processing apparatus, where the apparatusmay implement any one of the plurality of mobility management processingmethod embodiments provided in any one of the foregoing methods.

In a possible design, the apparatus includes a plurality of functionmodules, for example, including a processing unit and a transceiverunit, configured to implement the mobility management processing methodprovided above.

In a possible design, a structure of the apparatus includes a processorand a transceiver, where the processor is configured to support theapparatus in performing the corresponding functions in the mobilitymanagement processing method. The transceiver is configured to: supportcommunication between the apparatus and another apparatus, and receiveor send a message or an instruction in the mobility managementprocessing method from or to another apparatus. The apparatus mayfurther include a memory, where the memory is configured to be coupledto the processor, and the memory stores a program instruction and datathat are necessary for the apparatus.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

receiving, by a mobility management function AMF network element, afirst message that includes a paging area and that is sent by a sessionmanagement function SMF network element, where the paging area isdetermined by the SMF network element based on a session and servicecontinuity SSC mode and/or a service area of a user plane function UPFnetwork element, the SSC mode and/or the service area of the UPF networkelement are/is determined by the SMF network element based on anobtained protocol data unit PDU session identifier, and the UPF networkelement is a network element that establishes a PDU sessioncorresponding to the PDU session identifier; and

paging, by the AMF network element in the paging area, a terminal thatestablishes, by using the UPF network element, the PDU sessioncorresponding to the PDU session identifier.

According to the method provided in this embodiment of this application,after receiving the paging area sent by the SMF network element, the AMFnetwork element may page the terminal based on the paging area. Thepaging area is determined by the SMF network element terminal based onthe SSC mode corresponding to the PDU session identifier and/or theservice area of the UPF network element, and is smaller than or equal toan area indicated by a tracking area list of the terminal correspondingto the PDU session, so that whether the terminal can be successfullypaged can be more quickly determined, thereby improving accessefficiency of the terminal.

Optionally, the paging, by the AMF network element in the paging area, aterminal that establishes, by using the UPF network element, the PDUsession corresponding to the PDU session identifier includes:

sending, by the AMF network element, a second message to a radio accessnetwork network element, where the second message includes a pagingarea, and the second message is used to trigger the radio access networknetwork element to page the terminal based on the paging area.

Optionally, the paging area in the second message is used by the radioaccess network network element to determine the paging area in which theradio access network network element pages the terminal.

Optionally, the first message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times is usedto indicate a quantity of times of paging the terminal;

a paging cycle, where the paging cycle is used to indicate a cycle ofpaging the terminal; and

paging indication information, where the paging indication informationis used to indicate a manner of paging the terminal.

Optionally, the paging indication information indicates that if nopaging response is received in the paging area, the AMF network elementpages the terminal in the area indicated by the tracking area list.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

receiving, by a session management function SMF network element, a datanotification message that includes a protocol data unit PDU sessionidentifier and that is sent by a user plane function UPF networkelement, and determining, based on the PDU session identifier, at leastone of a session and service continuity SSC mode corresponding to thePDU session identifier and a service area of the UPF network element,where the UPF network element is a network element that establishes aPDU session corresponding to the PDU session identifier; and

sending, by the SMF network element, a first message to an access andmobility management function AMF network element, where the firstmessage includes at least one of the SSC mode and the service area, andthe first message is used to trigger the AMF network element to page aterminal that establishes the PDU session by using the UPF networkelement.

Optionally, the method further includes:

starting, by the SMF network element, a first timer; and

if it is determined after the first timer times out that no pagingresponse is received, discarding, by the SMF network element, a downlinkdata packet received from the terminal.

Based on a same inventive concept, an embodiment of this applicationprovides a mobility management processing apparatus, where the apparatusmay implement any one of the plurality of mobility management processingmethod embodiments provided in any one of the foregoing methods.

In a possible design, the apparatus includes a plurality of functionmodules, for example, including a processing unit and a transceiverunit, configured to implement the mobility management processing methodprovided above.

In a possible design, a structure of the apparatus includes a processorand a transceiver, where the processor is configured to support theapparatus in performing the corresponding functions in the mobilitymanagement processing method. The transceiver is configured to: supportcommunication between the apparatus and another apparatus, and receiveor send a message or an instruction in the mobility managementprocessing method from or to another apparatus. The apparatus mayfurther include a memory, where the memory is configured to be coupledto the processor, and the memory stores a program instruction and datathat are necessary for the apparatus.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

receiving, by a mobility management function AMF network element, afirst message sent by a session management function SMF network element,where the first message includes at least one of a session and servicecontinuity SSC mode and a service area of a user plane function UPFnetwork element, the SSC mode and the service area are determined by theSMF network element based on an obtained protocol data unit PDU sessionidentifier, and the service area is a service area of the user planefunction UPF network element that establishes a PDU sessioncorresponding to the PDU session identifier; and

determining, by the AMF network element, a paging area based on at leastone of the SSC mode and the service area, and paging, in the pagingarea, a terminal that establishes the PDU session by using the UPFnetwork element.

Optionally, the determining, by the AMF network element, a paging areabased on at least one of the SSC mode and the service area includes:

if it is determined that the SSC mode is an SSC mode 1, determining, bythe AMF network element as the paging area, an area indicated by atracking area list; or

if it is determined that the SSC mode is an SSC mode 2 or an SSC mode 3,determining, by the AMF network element, the service area as the pagingarea, or determining an overlapping area of the service area and atracking area list as the paging area.

Optionally, the paging, by the AMF network element in the paging area, aterminal that establishes the PDU session by using the UPF networkelement includes:

sending, by the AMF network element, a second message to a radio accessnetwork network element, where the second message includes a pagingarea, and the second message is used to trigger the radio access networknetwork element to page the terminal based on the paging area.

Optionally, the second message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times is usedto indicate a quantity of times for which the radio access networknetwork element pages the terminal;

a paging cycle, where the paging cycle is used to indicate a cycle inwhich the radio access network network element pages the terminal; and

paging indication information, where the paging indication informationis used to indicate a manner in which the radio access network networkelement pages the terminal.

Optionally, the paging indication information indicates that if nopaging response is received in the paging area, the radio access networknetwork element pages the terminal in the area indicated by the trackingarea list.

Based on a same inventive concept, an embodiment of this applicationprovides a mobility management processing apparatus, where the apparatusmay implement any one of the plurality of mobility management processingmethod embodiments provided in any one of the foregoing methods.

In a possible design, the apparatus includes a plurality of functionmodules, for example, including a processing unit and a transceiverunit, configured to implement the mobility management processing methodprovided above.

In a possible design, a structure of the apparatus includes a processorand a transceiver, where the processor is configured to support theapparatus in performing the corresponding functions in the mobilitymanagement processing method. The transceiver is configured to: supportcommunication between the apparatus and another apparatus, and receiveor send a message or an instruction in the mobility managementprocessing method from or to another apparatus. The apparatus mayfurther include a memory, where the memory is configured to be coupledto the processor, and the memory stores a program instruction and datathat are necessary for the apparatus.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

receiving, by a session management function SMF network element, a datanotification message that includes a protocol data unit PDU sessionidentifier and that is sent by a user plane function UPF networkelement, where the PDU session identifier is an identifier of a PDUsession that corresponds to the PDU session identifier and that isestablished by a terminal by using the UPF network element;

determining, by the SMF network element, the service area of the UPFnetwork element and a session and service continuity SSC mode of the PDUsession based on the PDU session identifier; and

determining, by the SMF network element based on the service area andthe SSC mode of the PDU session, whether to trigger establishment of auser-plane transmission channel.

Optionally, the determining, by the SMF network element based on theservice area and the SSC mode of the PDU session, whether to triggerestablishment of a user-plane transmission channel includes:

if it is determined that the SSC mode of the PDU session is an SSC mode2, and that the terminal is located in the service area, triggering, bythe SMF network element, establishment of the user-plane transmissionchannel; or

if it is determined that the SSC mode of the PDU session is an SSC mode2, and that the terminal is not located in the service area, ignoring,by the SMF network element, the data notification message.

Optionally, after the ignoring, by the SMF network element, the datanotification message, the method further includes:

sending, by the SMF, packet discard indication information to the UPFnetwork element, where the packet discard indication information is usedto instruct the UPF network element to discard downlink data receivedfrom the terminal.

Based on a same inventive concept, an embodiment of this applicationprovides a mobility management processing apparatus, where the apparatusmay implement any one of the plurality of mobility management processingmethod embodiments provided in any one of the foregoing methods.

In a possible design, the apparatus includes a plurality of functionmodules, for example, including a processing unit and a transceiverunit, configured to implement the mobility management processing methodprovided above.

In a possible design, a structure of the apparatus includes a processorand a transceiver, where the processor is configured to support theapparatus in performing the corresponding functions in the mobilitymanagement processing method. The transceiver is configured to: supportcommunication between the apparatus and another apparatus, and receiveor send a message or an instruction in the mobility managementprocessing method from or to another apparatus. The apparatus mayfurther include a memory, where the memory is configured to be coupledto the processor, and the memory stores a program instruction and datathat are necessary for the apparatus.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

receiving, by a mobility management function AMF network element,protocol data unit PDU session information sent by a session managementfunction SMF network element, where the PDU session information includesat least one of an SSC mode of a first PDU session and a service area ofa user plane function UPF network element that establishes the first PDUsession; and

determining, by the AMF network element based on the PDU sessioninformation, an area indicated by a tracking area list.

Optionally, after the determining, by the AMF network element based onthe PDU session information, an area indicated by a tracking area list,the method further includes:

sending, by the AMF network element, the tracking area list to aterminal.

Based on a same inventive concept, an embodiment of this applicationprovides a mobility management processing apparatus, where the apparatusmay implement any one of the plurality of mobility management processingmethod embodiments provided in any one of the foregoing methods.

In a possible design, the apparatus includes a plurality of functionmodules, for example, including a processing unit and a transceiverunit, configured to implement the mobility management processing methodprovided above.

In a possible design, a structure of the apparatus includes a processorand a transceiver, where the processor is configured to support theapparatus in performing the corresponding functions in the mobilitymanagement processing method. The transceiver is configured to: supportcommunication between the apparatus and another apparatus, and receiveor send a message or an instruction in the mobility managementprocessing method from or to another apparatus. The apparatus mayfurther include a memory, where the memory is configured to be coupledto the processor, and the memory stores a program instruction and datathat are necessary for the apparatus.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

obtaining, by a session management function SMF network element, aprotocol data unit PDU session identifier of a terminal and locationinformation of the terminal; and

if it is determined, based on the PDU session identifier and thelocation information of the terminal, to reselect a UPF network elementof the first PDU session corresponding to the PDU session identifier,triggering, by the SMF network element by using a mobility managementfunction AMF network element, the terminal to initiate a process ofestablishing a second PDU session.

Optionally, the triggering, by the SMF network element by using amobility management function AMF network element, the terminal toestablish a second PDU session includes:

determining, by the SMF network element, PDU session status information,and sending the PDU session status information to the terminal by usingthe AMF network element, where the PDU session status informationinstructs the terminal to initiate the process of establishing thesecond PDU session.

Optionally, the method further includes:

receiving, by the SMF network element, a data notification message thatincludes application information and that is sent by the UPF networkelement of the first PDU session, where the data notification message issent after the UPF network element of the first PDU session receives adownlink data packet from the terminal.

Optionally, the method further includes:

sending, by the SMF network element, the application information to theAMF network element, where the application information is used to notifythe terminal of application information used for triggering a pagingprocess.

Based on a same inventive concept, an embodiment of this applicationprovides a mobility management processing apparatus, where the apparatusmay implement any one of the plurality of mobility management processingmethod embodiments provided in any one of the foregoing methods.

In a possible design, the apparatus includes a plurality of functionmodules, for example, including a processing unit and a transceiverunit, configured to implement the mobility management processing methodprovided above.

In a possible design, a structure of the apparatus includes a processorand a transceiver, where the processor is configured to support theapparatus in performing the corresponding functions in the mobilitymanagement processing method. The transceiver is configured to: supportcommunication between the apparatus and another apparatus, and receiveor send a message or an instruction in the mobility managementprocessing method from or to another apparatus. The apparatus mayfurther include a memory, where the memory is configured to be coupledto the processor, and the memory stores a program instruction and datathat are necessary for the apparatus.

An embodiment of this application provides a mobility managementprocessing method, where the method includes:

receiving, by a session management function SMF network element, servicerestriction area information sent by a mobility management function AMFnetwork element; and

selecting, by the SMF, a user plane function UPF network element for aterminal based on the service restriction area information, where theUPF network element is configured to establish a PDU session for theterminal.

An embodiment of this application further provides a mobility managementprocessing apparatus. The apparatus includes a processor and a memory.The memory is configured to store a software program, and the processoris configured to: read the software program stored in the memory andimplement the mobility management processing method provided in any oneof the foregoing designs. The apparatus may be a mobile terminal, acomputer, or the like.

An embodiment of this application further provides a computer storagemedium, where the storage medium stores a software program. When beingread and executed by one or more processors, the software program canimplement the mobility management processing method provided in any oneof the foregoing designs.

An embodiment of this application further provides a communicationssystem, where the system includes the mobility management processingapparatus provided in any one of the foregoing designs. Optionally, thesystem may further include another device that interacts with themobility management processing apparatus in the solution provided inthis embodiment of this application.

An embodiment of this application further provides a computer programproduct including an instruction. When the computer program product runson a computer, the computer performs the methods in the foregoingaspects.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a first possible 5G networkarchitecture;

FIG. 2 is a schematic diagram of a second possible 5G networkarchitecture;

FIG. 3 is a schematic diagram of a third possible 5G networkarchitecture;

FIG. 4 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application;

FIG. 5 is a schematic diagram of a tracking area update procedureaccording to an embodiment of this application;

FIG. 6 is a schematic diagram of a mobility management processingprocess according to an embodiment of this application;

FIG. 7 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application;

FIG. 8 is a schematic diagram of a mobility management processingprocess according to an embodiment of this application;

FIG. 9 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application;

FIG. 10 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application;

FIG. 11 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application;

FIG. 12 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application;

FIG. 13 is a schematic diagram of a service restriction area accordingto an embodiment of this application;

FIG. 14 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application;

FIG. 15 is a schematic diagram of a PDU session establishment procedureaccording to an embodiment of this application;

FIG. 16 is a schematic diagram of a PDU session establishment procedureaccording to an embodiment of this application;

FIG. 17 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application;

FIG. 18 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application;

FIG. 19 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application;

FIG. 20 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application;

FIG. 21 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application;

FIG. 22 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application;

FIG. 23 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application; and

FIG. 24 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

The following further describes the embodiments of this application indetail with reference to the accompanying drawings.

The embodiments of this application may be applied to various mobilecommunications systems, such as a global system for mobilecommunications (Global System of Mobile communication, GSM), a codedivision multiple access (Code Division Multiple Access, CDMA) system, awideband code division multiple access (Wideband Code Division MultipleAccess, WCDMA) system, a general packet radio service (General PacketRadio Service, GPRS) system, a long term evolution (Long Term Evolution,LTE) system, a long term evolution advanced (Advanced long termevolution, LTE-A) system, a universal mobile telecommunications system(Universal Mobile Telecommunication System, UMTS), an evolved long termevolution (evolved Long Term Evolution, eLTE) system, a 5G system (forexample, an NR system), and other mobile communications systems.

There are a plurality of possible 5G network architectures that arebeing discussed. FIG. 1 to FIG. 3 are schematic diagrams of first tothird possible 5G network architectures, respectively. In the networkarchitecture shown in FIG. 1, there is one UPF network element between aRAN network element and a DN network element. In the networkarchitecture shown in FIG. 2, there are two UPF network elementsconnected in parallel between a RAN network element and a DN networkelement. In the network architecture shown in FIG. 1, there are two UPFnetwork elements connected in series between a RAN network element and aDN network element.

Systems shown in FIG. 1 to FIG. 3 include an authentication serverfunction (Authentication Server Function, AUSF) network element, aunified database management (Unified Data Management, UDM) function, anaccess and mobility management function (Access and Mobility ManagementFunction, AMF) network element, a session management function (SessionManagement Function, SMF) network element, a policy control function(Policy Control function, PCF) network element, an AF network element, aradio access network (Radio Access Network, RAN) network element (whichmay also be referred to as an access network (Access Network, AN)network element), a UPF network element, a DN network element, and thelike. The SMF network element is responsible for session management,allocation and management of an internet protocol (Internet Protocol,IP) address of a terminal, allocation and selection of a UP anchorfunction, selection (or reselection) of the UPF and a user plane path,and the like. The AMF network element is responsible for access andmobility management, is a termination point of an NG2 interface (aninterface between an AMF and a RAN device), terminates a NAS message,completes registration management, connection management andreachability management, TA list allocation, mobility management, andthe like, and transparently routes a session management (SessionManagement, SM) message to the SMF network element. The UPF networkelement is a user plane function device, and is responsible forfunctions such as routing and forwarding a data packet, lawfulinterception, caching a downlink data packet, and triggering a downlinkdata packet notification message.

In addition, it should be noted that in the embodiments of thisapplication, a terminal, also referred to as user equipment (UserEquipment, terminal), is a device that provides voice and/or dataconnectivity for a user, such as a handheld device or an in-vehicledevice with a wireless connection function. Common terminals include,for example, a mobile phone, a tablet computer, a notebook computer, apalmtop computer, a mobile internet device (mobile internet device,MID), and a wearable device, such as a smartwatch, a smart band, or apedometer.

Based on the foregoing description, FIG. 4 is a schematic flowchart of amobility management processing method according to an embodiment of thisapplication. The method includes the following steps.

Step 401: An SMF network element receives a data notification messagethat includes a PDU session identifier and that is sent by a UPF networkelement, and determines, based on the PDU session identifier, an SSCmode corresponding to the PDU session identifier and/or a service areaof the UPF network element, where the UPF network element is a networkelement that establishes a PDU session corresponding to the PDU sessionidentifier.

Step 402: The SMF network element determines a paging area based on theSSC mode and/or the service area of the UPF network element.

The paging area determined by the SMF network element is smaller than orequal to an area indicated by a tracking area list of a terminalcorresponding to the PDU session.

Step 403: The SMF network element sends a first message including thepaging area to an access and AMF network element, where the firstmessage is used to trigger the AMF network element to page, in thepaging area, the terminal that establishes the PDU session by using theUPF network element.

Step 404: The AMF network element receives the first message thatincludes the paging area and that is sent by the SMF network element,where the paging area is determined by the SMF network element based onthe SSC mode and/or the service area of the user plane function UPFnetwork element.

The SSC mode and/or the service area of the UPF network element are/isdetermined by the SMF network element based on the obtained PDU sessionidentifier, and the UPF network element is a network element thatestablishes the PDU session corresponding to the PDU session identifier.

Step 405: The AMF network element pages, in the paging area, theterminal that establishes, by using the UPF network element, the PDUsession corresponding to the PDU session identifier.

In step 401, after the terminal establishes the PDU session, when thereis no non-access stratum (Non-Access Stratum, NAS) signaling connectionor data transmission between the terminal and the AMF network element,the terminal is in an idle state, and neither an N2 interface (aninterface between the AMF network element and a RAN network element)signaling connection nor an N3 interface (an interface between the RANnetwork element and the UPF network element) data (user plane)transmission channel connection exists. When the UPF network elementreceives a downlink data packet from the terminal, or a core networkdevice such as the UPF network element triggers a control signalingprocess, the UPF network element may determine a PDU session identifierof a PDU session to which the downlink data packet or control signalingbelongs.

After determining the PDU session identifier based on the downlink datapacket received from the terminal, the UPF network element may send thedata notification message including the PDU session identifier to theSMF network element, so as to instruct a network device (such as the SMFnetwork element/the AMF network element) network element to page theterminal, to send the downlink data packet to the terminal.

The PDU session identifier can uniquely identify a PDU session, the PDUsession is established by the terminal with a data network by using theUPF network element, and an SSC mode of each PDU session is determinedupon establishment of the PDU session. Therefore, the SMF networkelement may determine, based on the PDU session identifier, at least oneof the SSC mode corresponding to the PDU session identifier and theservice area of the UPF network element that establishes the PDU sessionidentifier.

In step 402, the SMF network element determines the paging area in aplurality of manners, and details are described below.

In a first possible paging area determining manner, if it is determinedthat the SSC mode of the PDU session corresponding to the PDU sessionidentifier is an SSC mode 2, the SMF network element may use, as thepaging area, the service area of the UPF network element thatestablishes the PDU session.

It should be noted that the paging area may be the same as or differentfrom the service area of the UPF network element. For example, the SMFnetwork element may determine, based on a historical location of theterminal, a historical area on which the terminal camps in the servicearea as the paging area. In this case, the paging area is smaller thanthe service area of the UPF network element.

In a second possible paging area determining manner, if it is determinedthat the SSC mode of the PDU session is an SSC mode 1 or an SSC mode 3,the SMF network element uses, as the paging area, the area indicated bythe tracking area list.

In a third possible paging area determining manner, the SMF networkelement determines the paging area based on the tracking area list andthe service area of the UPF network element. Specifically, the SMFnetwork element may determine, as the paging area, an overlapping areaof the service area and the area indicated by the tracking area list.

It should be noted that the tracking area list is allocated by amobility management network element (for example, the AMF networkelement), and indicates a location area. When moving within the areaindicated by the tracking area list, the terminal does not initiate atracking area update procedure. When leaving the area indicated by thetracking area list, the terminal initiates a tracking area updateprocedure. To initiate a tracking area update procedure is to enable amobile network to learn a location area of the terminal, so that amobility management process can be more effectively performed. In 5Gtechnical research, the tracking area update procedure may also bereferred to as a mobility registration update procedure. The terminaldevice registers a current location of the terminal device with anetwork side again through this procedure.

In this embodiment of this application, the AMF network element may sendthe tracking area list to the SMF network element after generating thetracking area list. A manner in which the AMF network element sends thetracking area list to the SMF network element is not limited in thisembodiment of this application. For example, the AMF network element maysend the tracking area list in a process in which the terminal registerswith a mobile communications network, or may send the tracking area listto the SMF network element in the tracking area update procedure of theterminal. Specifically, FIG. 5 is a schematic diagram of a tracking areaupdate procedure according to an embodiment of this application. In FIG.5, the tracking area update procedure includes the following steps.

Step 501: The terminal sends a tracking area update (Tracking AreaUpdate, TAU) or mobility registration update (Mobility RegistrationUpdate, MRU) request message to the AMF network element, to trigger thetracking area update procedure of the terminal.

Step 502: The AMF network element generates a tracking area list afterreceiving the TAU or MRU request message.

A specific manner in which the AMF network element generates thetracking area list is not limited in this embodiment of thisapplication.

Step 503: The AMF network element sends an SM request message includingthe tracking area list to the SMF network element. This step is intendedto notify the SMF network element of the tracking area list.

It should be noted that, in addition to the message, a process in whichthe AMF network element sends the tracking area list to the SMF networkelement may be performed in another message.

Step 504: The AMF network element sends a TAU accept message includingthe tracking area list to the terminal.

It should be noted that an order of performing step 503 and step 504 isnot limited.

Optionally, the SMF network element may further start a first timer,timing duration of the first timer is preset duration, and the presetduration may be determined depending on a specific case. This is notlimited in this embodiment of this application. If it is determinedafter the first timer times out that the AMF network element receives nopaging response, the SMF network element sends packet discard indicationinformation to the UPF network element, where if no service requestprocess triggered in a paging process is received within a specifictime, it may be considered that no paging response is received, and thepacket discard indication information is used to instruct the UPFnetwork element to discard a downlink data packet received from theterminal.

Optionally, the UPF network element may also start a second timer, forexample, start the second timer after receiving the downlink data packetfrom the terminal or sending the data notification message to the SMFnetwork element. If it is determined after the second timer times outthat the AMF network element receives no paging response, the UPFnetwork element discards the downlink data packet received from theterminal. Timing duration of the second timer may be determineddepending on a specific case. This is not limited in this embodiment ofthis application.

According to the foregoing method, if it is determined within a specifictime that the AMF network element receives no paging response from theterminal, the SMF network element instructs the UPF network element todiscard downlink data packets received from the terminal. Especially forthe PDU session in the SSC mode 2, if the terminal leaves the servicearea of the UPF network element, a UPF network element needs to bereselected for the PDU session, and an IP address of the terminal devicemay need to change. Consequently, the PDU session may be interrupted,and the data packets may no longer be sent to the terminal. Therefore,the data packets may be discarded, so that network resources of the UPFnetwork element can be saved, and system operation efficiency can beimproved.

It should be noted that, in this embodiment of this application, the SMFnetwork element may start the first timer after receiving the datanotification message, or may start the first timer when sending thefirst message to the AMF network element. Details may be determineddepending on an actual case. This is not limited in this embodiment ofthis application.

In step 403, the SMF network element may further send a paging policy tothe AMF network element by using the first message.

In this embodiment of this application, the paging policy may includeone or more of the following:

a quantity of paging times, where the quantity of paging times indicatesa quantity of times for which the AMF network element pages theterminal;

a paging cycle, where the paging cycle indicates a cycle in which theAMF network element pages the terminal; and

paging indication information, where the paging indication informationindicates a manner in which the AMF network element pages the terminal;for example, the paging indication information may indicate that if nopaging response is received in the paging area, the AMF network elementpages the terminal in the area indicated by the tracking area list.

Certainly, alternatively, the SMF network element may not send thepaging indication information, but implicitly instruct the AMF networkelement to page the terminal separately in the paging area and in thearea indicated by the tracking area list. For example, the SMF networkelement sends the first message including the paging area and thetracking area list to the AMF network element, so as to instruct the AMFnetwork element to page, if no paging response is received in the pagingarea, the terminal in the area indicated by the tracking area list.

It should be noted that the first message may further includeinformation such as the PDU session identifier. Details are notdescribed one by one herein.

After receiving the first message in step 404, the AMF network elementmay send a second message to a radio access network network element instep 405. The second message includes a paging area, and the secondmessage is used to trigger the radio access network network element topage the terminal based on the paging area. The radio access networknetwork element determines, based on some information about an accessnetwork, a paging area for paging the terminal, and the paging area sentby the AMF network element by using the second message may be only onefactor based on which the radio access network network elementdetermines the paging area for paging the terminal. Therefore, thepaging area in the second message may be different from the paging areain which the radio access network network element pages the terminal.Therefore, the paging area in the second message may be used by theradio access network network element to determine the paging area inwhich the radio access network network element pages the terminal.

Optionally, the AMF network element may further send information such asthe paging policy to the radio access network network element by usingthe second message, and finally the radio access network network elementmay page the terminal based on the paging area and the paging policy.

For a specific process in which the radio access network network elementpages the terminal, refer to description in the prior art. Details arenot described herein.

In this embodiment of this application, after sending the second messageto the radio access network network element, if the AMF determines thatthe radio access network network element receives no paging responsefrom the terminal in the paging area, the AMF may further instruct theradio access network network element to page the terminal in the areaindicated by the tracking area list.

The foregoing process is described below by using a specific embodiment.

FIG. 6 is a schematic diagram of a mobility management processingprocess according to an embodiment of this application. Before a pagingprocess shown in FIG. 6, a terminal establishes a PDU session with a DNnetwork element by using a UPF network element, and then the terminalenters an idle state.

Step 601: After receiving a downlink data packet of the PDU session, theUPF network element sends a data notification message to an SMF networkelement, where the data notification message includes information suchas a PDU session identifier of the PDU session.

Step 602: The SMF network element determines, based on the PDU sessionidentifier, the UPF network element that establishes a connection forthe PDU session corresponding to the PDU session identifier, anddetermines a paging area based on a service area of the UPF networkelement and an SSC mode of the PDU session.

For a specific method for determining the paging area, refer to theforegoing description. Details are not described herein again.

Optionally, the SMF network element may start a first timer; and if nopaging response is received after the first timer times out, the SMFnetwork element sends packet discard indication information to the UPFnetwork element.

Step 603: The SMF network element sends a first message to an AMFnetwork element, where the first message may include the PDU sessionidentifier, the paging area, a paging policy (Paging Policy), and thelike.

The first message may be referred to as an N11 message. The N11 messageis provisionally defined in an existing protocol, and may be changed inthe future.

Step 604: The AMF network element sends a second message to a radioaccess network network element, where the second message may include thepaging area, a tracking area list, a paging policy, and the like.

Step 605: The RAN network element sends a paging message to the terminalbased on information such as the paging area and/or the paging policy,so as to page the terminal.

According to the foregoing method, after receiving the data notificationmessage including the PDU identifier, the SMF network elementdetermines, based on the PDU identifier, the service area of the UPFnetwork element corresponding to the PDU identifier and the SSC mode, soas to determine the paging area based on the service area of the UPFnetwork element and the SSC mode, and instruct the AMF to page theterminal based on the paging area. The determined paging area is smallerthan or equal to the area indicated by the tracking area list of theterminal corresponding to the PDU session, so that whether the terminalcan be successfully paged can be more quickly determined, therebyimproving access efficiency of the terminal.

In this embodiment of this application, alternatively, the AMF networkelement may determine the paging area. Specifically, FIG. 7 is aschematic flowchart of a mobility management processing method accordingto an embodiment of this application. The method includes the followingsteps:

Step 701: An SMF network element receives a data notification messagethat includes a PDU session identifier and that is sent by a UPF networkelement, and determines, based on the PDU session identifier, at leastone of an SSC mode corresponding to the PDU session identifier and aservice area of the UPF network element, where the UPF network elementis a network element that establishes a PDU session corresponding to thePDU session identifier.

Step 702: The SMF network element sends a first message to the AMFnetwork element, where the first message includes at least one of theSSC mode and the service area, and the first message is used to triggerthe AMF network element to page a terminal that establishes the PDUsession by using the UPF network element.

Step 703: The AMF network element receives the first message sent by theSMF network element, where the first message includes at least one ofthe SSC mode and the service area of the UPF network element, the SSCmode and the service area are determined by the SMF network elementbased on the obtained PDU session identifier, and the service area is aservice area of the user plane function UPF network element thatestablishes the PDU session corresponding to the PDU session identifier.

Step 704: The AMF network element determines a paging area based on atleast one of the SSC mode and the service area, and pages, in the pagingarea, the terminal that establishes the PDU session by using the UPFnetwork element.

Optionally, the paging area is smaller than or equal to an areaindicated by a tracking area list of the terminal corresponding to thePDU session.

In step 701, after the terminal establishes the PDU session, when thereis no NAS signaling connection between the terminal and the AMF networkelement, the terminal is in an idle state. When the UPF network elementreceives a downlink data packet from the terminal, or a core networkdevice such as the UPF network element triggers a control signalingprocess, the UPF network element may determine a PDU session identifierof a PDU session to which the downlink data packet or control signalingbelongs.

After determining the PDU session identifier, the UPF network elementmay send the data notification message including the PDU sessionidentifier to the SMF network element, so as to notify the SMF networkelement that the terminal needs to be paged, to send the downlink datapacket to the terminal.

After receiving the data notification message including the PDU sessionidentifier, the SMF network element may determine, based on the PDUsession identifier, at least one of the SSC mode corresponding to thePDU session identifier and the service area of the UPF network elementthat establishes the PDU session identifier.

Optionally, the SMF network element may further start a first timer,timing duration of the first timer is preset duration, and the presetduration may be determined depending on a specific case. This is notlimited in this embodiment of this application. If it is determinedafter the first timer times out that no paging response is received, theSMF network element sends packet discard indication information to theUPF network element, where the packet discard indication information isused to instruct the UPF network element to discard the downlink datapacket received from the terminal.

Optionally, the UPF network element may also start a second timer, forexample, start the second timer after receiving the downlink data packetfrom the terminal or sending the data notification message to the SMFnetwork element. If it is determined after the second timer times outthat no paging response is received, the UPF network element discardsthe downlink data packet received from the terminal. Timing duration ofthe second timer may be determined depending on a specific case. This isnot limited in this embodiment of this application.

According to the foregoing method, if it is determined within a specifictime that the AMF network element receives no paging response from theterminal, the SMF network element instructs the UPF network element todiscard the downlink data packet received from the terminal, so thatnetwork resources of the UPF network element can be saved, and systemoperation efficiency can be improved.

In step 702, the first message sent by the SMF network element to theAMF network element may further include information such as the PDUsession identifier.

In step 703, the AMF network element determines the paging area in aplurality of manners, and details are described below.

In a first possible paging area determining manner, if it is determinedthat the SSC mode is an SSC mode 1, the AMF network element determines,as the paging area, the area indicated by the tracking area list.

In a second possible paging area determining manner, if it is determinedthat the SSC mode is an SSC mode 2 or an SSC mode 3, the AMF networkelement determines the service area as the paging area.

It should be noted that the paging area may be the same as or differentfrom the service area of the UPF network element. For example, the SMFnetwork element may determine, based on a historical location of theterminal, a historical area on which the terminal camps in the servicearea as the paging area. In this case, the paging area is smaller thanthe service area of the UPF network element.

In a third possible paging area determining manner, if it is determinedthat the SSC mode is an SSC mode 2 or an SSC mode 3, the AMF networkelement determines an overlapping area of the service area and thetracking area list as the paging area.

Optionally, the AMF may further determine a paging policy, and thepaging policy may include one or more of the following:

a quantity of paging times, where the quantity of paging times is usedto indicate a quantity of times for which a radio access network networkelement pages the terminal;

a paging cycle, where the paging cycle is used to indicate a cycle inwhich the radio access network network element pages the terminal; and

paging indication information, where the paging indication informationis used to indicate a manner in which the radio access network networkelement pages the terminal; for example, the paging indicationinformation indicates that if no paging response is received in thepaging area, the radio access network network element pages the terminalin the area indicated by the tracking area list. Certainly,alternatively, the AMF network element may not send the pagingindication information, but implicitly instruct the radio access networknetwork element to page the terminal separately in the paging area andin the area indicated by the tracking area list. For example, the AMFnetwork element sends a second message including the paging area and thetracking area list to the radio access network network element, so as toinstruct the radio access network network element to page, if no pagingresponse is received in the paging area, the terminal in the areaindicated by the tracking area list.

In step 704, the AMF network element may send the second message to theradio access network network element, where the second message includesa paging area, and the second message is used to trigger the radioaccess network network element to page the terminal based on the pagingarea.

Optionally, the second message may further include information such asthe PDU session identifier and the paging policy.

Finally, the radio access network network element performs paging basedon the paging area. For a specific paging process, refer to the priorart. Details are not described herein.

The foregoing process is described below by using a specific embodiment.

FIG. 8 is a schematic diagram of a mobility management processingprocess according to an embodiment of this application. Before a pagingprocess shown in FIG. 8, a terminal establishes a PDU session with a DNnetwork element by using a UPF network element, and then the terminalenters an idle state.

Step 801: After receiving a downlink data packet of the PDU session, theUPF network element sends a data notification message to an SMF networkelement, where the data notification message includes information suchas a PDU session identifier of the PDU session.

Step 802: The SMF network element determines, based on the PDU sessionidentifier, the UPF network element that establishes a connection forthe PDU session corresponding to the PDU session identifier and an SSCmode corresponding to the PDU session identifier.

Optionally, the SMF network element may start a first timer; and if itis determined after the first timer times out that an AMF networkelement receives no paging response, the SMF network element sendspacket discard indication information to the UPF network element.

Step 803: The SMF network element sends a first message to the AMFnetwork element, where the first message may include at least one of theSSC mode and a service area of the UPF network element.

The first message may further include the PDU session identifier. Thefirst message may also be referred to as an N11 message.

Step 804: The AMF network element determines a paging area based on atleast one of the SSC mode and the service area of the UPF networkelement.

For a specific process in which the AMF network element determines thepaging area, refer to the foregoing description. Details are notdescribed herein again.

Optionally, the AMF network element may further determine a pagingpolicy.

Step 805: The AMF network element sends a second message to a radioaccess network network element, where the second message may include thepaging area and a tracking area list.

Optionally, the second message may further include the paging policy.

Step 806: The RAN network element sends a paging message to the terminalbased on information such as the paging area and/or the paging policy,so as to page the terminal.

According to the foregoing method, after receiving the first messageincluding at least one of the SSC mode and the service area of the UPFnetwork element, the AMF network element determines the paging areabased on at least one of the SSC mode and the service area of the UPFnetwork element, and instructs the radio access network network elementto page the terminal based on the paging area. The determined pagingarea is smaller than or equal to an area indicated by the tracking arealist of the terminal corresponding to the PDU session, so that whetherthe terminal can be successfully paged can be more quickly determined,thereby improving access efficiency of the terminal.

In this embodiment of this application, after the terminal switches to aconnected state, the SMF network element may further determine whetherto trigger establishment of a user-plane transmission channel. Theterminal switches to a connected state in a plurality of cases,including but not limited to: a paging and service request processtriggered when a downlink data packet for one PDU session of theterminal is received, or a signaling process triggered by a network-sidedevice such as a PCF network element or the UPF network element.

Specifically, FIG. 9 is a schematic flowchart of a mobility managementprocessing method according to an embodiment of this application. Themethod includes the following steps:

Step 901: An SMF network element receives a data notification messagethat includes a PDU session identifier and that is sent by a UPF networkelement, where the PDU session identifier is an identifier of a PDUsession that corresponds to the PDU session identifier and that isestablished by a terminal by using the UPF network element.

Step 902: The SMF network element determines a service area of the UPFnetwork element and an SSC mode of the PDU session based on the PDUsession identifier.

Step 903: The SMF network element determines, based on the service areaand the SSC mode of the PDU session, whether to trigger establishment ofa user-plane transmission channel.

For specific content of step 901 and step 902, refer to the descriptionsin step 401 and step 402. Details are not described herein again.

In step 903, in a first possible implementation, if it is determinedthat the SSC mode of the PDU session is an SSC mode 2, and that theterminal is located in the service area, the SMF network elementtriggers establishment of the user-plane transmission channel.

In a second possible implementation, if it is determined that the SSCmode of the PDU session is an SSC mode 2, and that the terminal is notlocated in the service area, the SMF network element ignores the datanotification message.

In a third possible implementation, if it is determined that theterminal is located in the service area, the SMF network elementtriggers establishment of the user-plane transmission channel.

In a fourth possible implementation, if it is determined that the SSCmode of the PDU session is an SSC mode 1 or an SSC mode 3, and that theterminal is not located in the service area, the SMF network elementtriggers establishment of the user-plane transmission channel.

Optionally, after ignoring the data notification message, the SMFnetwork element may further send packet discard indication informationto the UPF network element, where the packet discard indicationinformation is used to instruct the UPF network element to discarddownlink data received from the terminal.

The foregoing process is described below by using a specific embodiment.

FIG. 10 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application. Before aprocedure shown in FIG. 10, the terminal has switched to a connectedstate.

Step 1001: After receiving a downlink data packet from a terminal, a UPFnetwork element sends a data notification message to an SMF networkelement, where the data notification message includes information suchas a PDU session identifier of a PDU session to which the downlink datapacket belongs.

Step 1002: The SMF network element determines, based on the PDU sessionidentifier, the UPF network element that establishes a connection forthe PDU session corresponding to the PDU session identifier and an SSCmode corresponding to the PDU session identifier, and determines, basedon a service area of the UPF network element and the SSC mode of the PDUsession, whether to trigger establishment of a user-plane transmissionchannel.

Specifically, if it is determined that the SSC mode of the PDU sessionis an SSC mode 2, and that the terminal is located in the service area,the SMF network element triggers establishment of the user-planetransmission channel, and performs step 1003 and steps following step1003.

In a second possible implementation, if it is determined that the SSCmode of the PDU session is an SSC mode 2, and that the terminal is notlocated in the service area, the SMF network element ignores the datanotification message, skips step 1003, and performs step 1004 and a stepfollowing step 1004. Optionally, the SMF network element may instructthe UPF network element to discard the downlink data packet receivedfrom the terminal, and the subsequent steps are not to be performed.

In a third possible implementation, if it is determined that theterminal is located in the service area, the SMF network elementtriggers establishment of the user-plane transmission channel, andperforms step 1003 and steps following step 1003.

In a fourth possible implementation, if it is determined that the SSCmode of the PDU session is an SSC mode 1 or an SSC mode 3, and that theterminal is not located in the service area, the SMF network elementtriggers establishment of the user-plane transmission channel, andperforms step 1003 and steps following step 1003.

Step 1003: The SMF network element sends a data notificationacknowledgement message to the UPF network element.

Optionally, the data notification acknowledgement message includespacket discard indication information.

Step 1004: The SMF network element sends an N11 message to an AMFnetwork element, where the N11 message is used to trigger establishmentof the data transmission channel between the UPF and a RAN device of thePDU session of the received downlink data packet.

Step 1005: The AMF network element sends an N11 acknowledgement messageto the SMF network element.

An embodiment of this application further provides a method forgenerating a tracking area list. Specifically, FIG. 11 is a schematicflowchart of a mobility management processing method according to anembodiment of this application. The method includes the following steps:

Step 1101: An AMF network element receives PDU session information sentby an SMF network element, where the PDU session information includes atleast one of an SSC mode of a first PDU session and a service area of aUPF network element that establishes the PDU session.

Step 1102: The AMF network element determines, based on the PDU sessioninformation, an area indicated by a tracking area list.

In step 1101, the AMF network element may receive, in a plurality ofcases, the PDU session information sent by the SMF network element. Forexample, after a terminal initiates a registration process ofestablishing the first PDU session, the SMF determines the PDU sessioninformation based on the established first PDU session, and sends thePDU session information to the AMF network element.

In step 1102, if it is determined that the SSC mode of the first PDUsession is an SSC mode 2, the AMF network element uses the service areaas the area indicated by the tracking area list.

If the AMF network element determines that the SSC mode of the first PDUsession is an SSC mode 2, the PDU session information includes an SSCmode of a second PDU session, and the SSC mode of the second PDU sessionis an SSC mode 1 or an SSC mode 3, the determined area indicated by thetracking area list includes a first-level area and a second-level area.The first-level area is an area indicated by a tracking area listexclusively used by the first PDU session, and the second-level area isan area indicated by a tracking area list shared by the first PDUsession and the second PDU session. The first-level area may be theservice area of the UPF corresponding to the first PDU session.

Optionally, the AMF network element may further send the tracking arealist to the terminal. The terminal may subsequently determine, based onthe PDU session information, to trigger a tracking area updateprocedure.

In this embodiment of this application, if the terminal has the firstPDU session whose SSC mode is an SSC mode 2, the terminal triggers thetracking area update procedure when determining to leave the areaindicated by the tracking area list exclusively used by the first PDUsession. If the terminal has only the second PDU session whose SSC modeis an SSC mode 1 or an SSC mode 3, the terminal does not trigger thetracking area update procedure when determining to leave the areaindicated by the tracking area list exclusively used by the first PDUsession.

Optionally, the terminal does not initiate a location area updateprocess when moving within an overlapping area of the first-level areaand the second-level area.

The foregoing process is described below by using a specific embodiment.

FIG. 12 is a schematic flowchart of a mobility management processingmethod according to an embodiment of this application. A procedure shownin FIG. 12 is described by using an example of a registration process ofestablishing a PDU session (for example, two PDU sessions areestablished in the registration process), but this embodiment of thisapplication is not limited to the process.

Step 1 to step 4 are the same as steps in the prior art.

Step 1201: A terminal initiates a registration request message, torequest to establish a PDU session.

Step 1202: A RAN network element selects an AMF network element for theterminal.

Step 1203: The RAN network element sends a registration request to theAMF network element.

Step 1204: The AMF network element selects an SMF network element forthe terminal.

Step 1205: The AMF network element sends an SM request to the SMFnetwork element, where the SM message includes location information ofthe terminal and service area restriction (Service AreaRestriction/Mobility Restriction area).

The service area restriction is an area in which a communication serviceof a terminal is restricted. In this area, the terminal cannot establishany signaling/data connection to a mobile communications network, orrespond to a service such as paging initiated by a network.

Step 1206: The SMF network element selects a UDM network element.

Step 1207: The SMF network element requests subscription data from theUDM network element, where the subscription data includessession-related subscription data.

Step 1208: The SMF network element selects a UPF network element basedon a location of the terminal and further based on the service arearestriction.

Step 1209 and step 1210: Establish a PDU session, where establishment ofa PDU session 1 and a PDU session 2 is used as an example.

Step 1211: The SMF network element sends a PDU session establishmentrequest acknowledgement message to the AMF network element, where themessage includes PDU session information, and the PDU sessioninformation includes an SSC mode of the PDU session and/or a servicearea of the UPF.

Step 1212: The AMF network element generates a tracking area list basedon the PDU session information, where a specific manner of generatingthe tracking area list may include, but is not limited to:

Manner a: If the PDU session is in an SSC mode 2, the service area ofthe UPF network element corresponding to the PDU session may be used asan area indicated by the tracking area list.

Manner b: If the PDU session is in an SSC mode 2 and an SSC mode 1 or anSSC mode 3, an area indicated by the generated tracking area list mayinclude a first-level area and a second-level area, and when thetracking area list is generated, the service area of the UPF networkelement of the PDU session in the SSC mode 2 is independently used asthe area indicated by the tracking area list of the PDU session.

Step 1213: The AMF network element sends a registration accept messageto the terminal, where the message includes tracking area listinformation.

Step 1214: The terminal sends a registration complete message to the AMFnetwork element.

If two levels of tracking area lists are generated in the manner b, ifthe two levels of tracking area lists have an overlapping area, theterminal does not initiate a location area update process when movingwithin the overlapping area; otherwise, the terminal initiates alocation area update process.

With reference to the foregoing description, in this embodiment of thisapplication, the SMF network element may receive service restrictionarea information sent by the AMF network element. Then the SMF networkelement may select, for the terminal based on the service restrictionarea information, the UPF network element that establishes the PDUsession for the terminal.

Specifically, the SMF network element may determine at least one UPFnetwork element based on location information of the terminal. Each ofthe at least one UPF network element may be a UPF network element whoseservice area covers a location indicated by the location information ofthe terminal. Certainly, the at least one UPF network element may befurther determined in another manner. This is not limited herein.

The SMF network element may determine, as the UPF network elementestablishing the PDU session, a UPF network element that is in the atleast one UPF network element and whose service area least overlaps anarea indicated by the service restriction area information.

For example, FIG. 13 is a schematic diagram of a service restrictionarea according to an embodiment of this application. In FIG. 13, aterminal 1304 is located in both a coverage area of a service area 1301of a UPF network element 1 and a coverage area of a service area 1302 ofa UPF network element 2. Therefore, one of the UPF network element 1 andthe UPF network element 2 may be used as a UPF network element used bythe terminal 1304 to establish a PDU session. In addition, a servicerestriction area 1303 of the terminal 1304 is located in the coveragearea of the service area 1302 of the UPF network element 2. Therefore,the UPF network element 1 may be determined as the UPF network elementused by the terminal 1304 to establish the PDU session. The terminal1304 may perceive a service restriction area, and a network side mayimplicitly perceive a motion track of the terminal 1304. For example,the terminal 1304 may not move to the area of the UPF network element 2because the service restriction area is in the area, but there is a highpossibility that the terminal 1304 moves to the area of the UPF networkelement 1. Therefore, it is better to select the UPF network element 1rather than the UPF network element 2 for the terminal 1304.

Currently, after the terminal establishes a PDU session with a DNnetwork element by using a first UPF network element, if the terminalmoves out of a service area of the first UPF network element, if anetwork side pages the terminal in the area indicated by the trackingarea list configured for the terminal, the terminal initiates a servicerequest process based on the prior art after receiving a paging message.In the process, a data transmission channel of the terminal is restored,and a downlink data packet (including a cached data packet) received bythe first UPF network element may be sent to the terminal by using thedata transmission channel.

However, for some scenarios, the first UPF network element caches anapplication data packet, and an application on a DN network element sideconsiders that a data packet is sent to the terminal by using the firstUPF network element. However, when the terminal moves out of the servicearea of the first UPF network element, the network side may reselect,according to a reselection principle of the UPF network element, a UPFnetwork element serving the terminal. Therefore, after the mobilenetwork side reselects a second UPF network element for the terminal, ifthe application on the DN network element side cannot performperception, the data packet is still sent to the first UPF networkelement. Therefore, the data packet cannot be sent to the terminal.Consequently, a service cannot be normally performed. In addition, evenif the reselected UPF network element is still the first UPF networkelement, the first UPF network element may reallocate an IP address tothe terminal. Therefore, the IP address of the terminal also changes.For the application, if a previous IP address of the terminal is stillused as a target address of the data packet, the data packet cannot benormally sent to the terminal either.

In conclusion, even if the network side uses a paging process to enablethe terminal to initiate the service request process, reselects a newUPF network element for the terminal, and establishes a new data packettransmission channel, the downlink data cannot be sent to the terminal,and the terminal cannot perceive the application that is of the downlinkdata packet and that triggers paging either. Therefore, the terminalcannot actively initiate a relationship with the application either, toimplement data transmission.

Certainly, the terminal may initiate the service request process notonly when the terminal is paged. If a terminal in an idle state activelyinitiates a service, the terminal also initiates the service requestprocess. When the terminal initiates the service request process, anetwork-side device (the SMF/the AMF) may obtain location information ofthe terminal. Based on PDU session information of a current terminal,for example, if there is a PDU session in an SSC mode 2, and a locationof the terminal is not within a service area of a UPF device of thesession, the network side may reselect a UPF device for the PDU session,and the terminal is notified to initiate a PDU session establishmentprocess.

Based on the foregoing description, FIG. 14 is a schematic diagram of amobility management processing method according to an embodiment of thisapplication.

Referring to FIG. 14, the method includes the following steps:

Step 1401: An SMF network element obtains a PDU session identifier of aterminal and location information of the terminal.

Step 1402: If it is determined, based on the PDU session identifier andthe location information of the terminal, to reselect a UPF networkelement of a first PDU session corresponding to the PDU sessionidentifier, the SMF network element triggers, by using an AMF networkelement, the terminal to initiate a process of establishing a second PDUsession.

In step 1401, the SMF network element may receive the PDU sessionidentifier of the terminal and the location information of the terminalthat are sent by the AMF network element.

For example, after receiving a downlink data packet from the terminal,the UPF network element of the first PDU session sends a datanotification message to the SMF network element, so that the SMF networkelement triggers the AMF network element to page the terminal. The datanotification message may include the PDU session identifier of the firstPDU session to which the downlink data packet belongs. After the AMFnetwork element pages the terminal, the terminal may initiate a servicerequest process by using the AMF network element, so as to obtain thelocation information of the terminal, and send the obtained PDU sessionidentifier and the obtained location information to the SMF networkelement.

Optionally, the data notification message sent by the UPF networkelement of the first PDU session to the SMF network element may furtherinclude application information. Therefore, the SMF network element mayreceive the data notification message that includes the applicationinformation and that is sent by the UPF network element of the first PDUsession. The application information may be application identifierinformation of the downlink data packet received by the UPF networkelement, or may be downlink data packets received by one or more UPFnetwork elements. The data notification message is sent after the UPFnetwork element of the first PDU session receives the downlink datapacket from the terminal.

In this embodiment of this application, the SMF network element mayfurther send the application information to the AMF network element,where the application information is used to notify the terminal of theapplication information used for triggering a paging process.

In step 1402, the SMF network element may trigger, in the followingmanner, the terminal to establish a second PDU session:

first determining, by the SMF network element, PDU session statusinformation instructing the terminal to initiate the process ofestablishing the second PDU session, and sending the PDU session statusinformation to the terminal by using the AMF network element, so as totrigger the terminal to initiate the process of establishing the secondPDU session.

The PDU session status information may be determined by the SMF networkelement. For example, the SMF network element determines that the UPFnetwork element of the PDU session needs to be reselected, so as todetermine that a state of the PDU session is not available (Notavailable). The PDU session identifier and the PDU session statusinformation are sent to the AMF network element, so that the AMF networkelement obtains status information of the PDU session, and notifies theterminal of the status information.

The SMF network element may determine the PDU session status informationin another manner: When the SMF network element determines that the UPFnetwork element of the PDU session needs to be reselected, the SMFnetwork element initiates a process of releasing an original PDUsession. The process of releasing the PDU session can be perceived bythe AMF network element. For example, the SMF network element instructsthe AMF network element to initiate the process of releasing the PDUsession, to instruct a RAN network element to release a related datatransmission channel. In the process, the AMF network element canperceive that the PDU session identified by the PDU session identifieris released. In other words, the PDU session status information of thesession is not available. In this scenario, it may also be consideredthat the SMF network element determines the PDU session statusinformation, and notifies the AMF network element of the PDU sessionstatus information.

After the terminal initiates the process of establishing the second PDUsession, the network side may establish a new PDU session, namely, thesecond PDU session, for the terminal, so that the terminal can establisha connection to an application again, a service can be normallyperformed, system efficiency can be improved, and user experience can beimproved.

It should be noted that the network side may establish the second PDUsession for the terminal by using the UPF network element of the firstPDU session, or may determine one UPF network element for the terminalagain to establish the second PDU session. This is not limited in thisembodiment of this application.

The foregoing process is specifically described below.

FIG. 15 is a schematic diagram of a PDU session establishment procedureaccording to an embodiment of this application.

Step 1501: A UPF network element receives a downlink data packet.

Step 1502: The UPF network element sends a data notification message toan SMF network element, where the data notification message includesinformation such as a PDU session identifier. The PDU session identifiercorresponds to a first PDU session.

Step 1503: The SMF network element sends an N11 message to an AMFnetwork element, where the N11 message includes the PDU sessionidentifier, SM information, and the like.

Step 1504: The AMF network element pages a terminal.

Step 1505: After the terminal to which the downlink data packet belongsreceives a paging message, the terminal sends a service request messageto the AMF network element, to initiate a service request process toestablish a data transmission channel between the terminal and the UPFnetwork element.

Step 1506: The AMF network element sends an N11 message to the SMFnetwork element, where the N11 message includes information such as thePDU session identifier, and may also include location information of theterminal. The SMF network element may determine to reselect a UPFnetwork element for the PDU session of the terminal, for example, basedon the location information of the terminal. In this case, the SMFnetwork element determines PDU session status information such as anindication that a current PDU session is not available. A specific formis not limited.

Step 1507: The SMF network element sends a message to the AMF networkelement, where the N11 message includes data transmission channelinformation on a core network side, so as to establish a datatransmission channel to a RAN network element side.

Step 1508: The AMF network element sends an N2 request message to a RANnetwork element, where the N2 request message includes NAS servicerequest accept information, the information may include the PDU sessionstatus information, PDU session information may indicate that the PDUsession is not available and the like, and a specific form is notlimited.

Optionally, in this step, if the AMF network element starts a timer, theN2 request message may also include timer information.

Step 1509: The RAN network element sends a radio resource control (RadioResource Control, RRC) connection reconfiguration process to theterminal, and in this process, the RAN network element side may notifythe terminal of the PDU session status information and/or the timerinformation received in step 1508.

Step 1510: The RAN network element sends an N2 request acknowledgementmessage.

Step 1511: The AMF network element sends the N11 message.

Step 1512 a: The SMF network element sends an N4 session update requestto the UPF network element of the first PDU session.

Step 1512 b: The UPF network element of the first PDU session sends anN4 session update response to the SMF network element.

Step 1510 to step 1512 b are the same as steps in the prior art, and areperformed to restore a data transmission channel between the terminaland the UPF network element of the first PDU session.

After the data transmission channel is established, the downlink datapacket received by the UPF is sent to the terminal device, so that theterminal device can perceive information about an application sendingdownlink data, such as an application name or application serverinformation.

Step 1513: The SMF network element sends an N11 message acknowledgementmessage to the AMF network element, where if no PDU session statusinformation is included in step 1508, the PDU session information may beincluded in this step.

Step 1514: The AMF network element sends a NAS message to the terminal,where the NAS message includes the PDU session status information.

After the terminal receives the session status information, the terminalmay initiate, based on an indication of the session status information,a new process of establishing the second PDU session. A specific form ofthe PDU session information is not limited, and may be that the firstPDU session is not available, the PDU session is established again, orthe like.

If the terminal further receives the timer information in step 1508, atimer may be started based on duration in the timer information, so asto complete step 1510 to step 1513 in the foregoing figure.

After the terminal initiates establishment of the second PDU session,the network side may select a corresponding UPF network element based oncurrent location information of the terminal, to establish a datatransmission channel between the terminal and a data network. Theterminal determines, based on the received downlink data packet, theinformation about the application communicating with the terminal, sothat the terminal may establish, by using the second PDU session, acommunication relationship with the application corresponding to theapplication information.

FIG. 16 is a schematic diagram of a PDU session establishment procedureaccording to an embodiment of this application.

Step 1601: A UPF network element receives a downlink data packet.

Step 1602: The UPF network element sends a data notification message toan SMF network element, where the data notification message includesinformation such as a PDU session identifier. The PDU session identifiercorresponds to a first PDU session.

The data notification message may further include applicationinformation. A specific form of the application information is notlimited, and may be information such as some or all cached data packetsor an application identifier.

Step 1603: The SMF network element sends an N11 message to an AMFnetwork element, where the N11 message includes the PDU sessionidentifier, SM information, and the like.

Step 1604: The AMF network element pages a terminal.

Step 1605: After the terminal to which the downlink data packet belongsreceives a paging message, the terminal sends a service request messageto the AMF network element, to initiate a service request process toestablish a data transmission channel between the terminal and the UPFnetwork element.

Step 1606: The AMF network element sends an N11 message to the SMFnetwork element, where the N11 message includes the PDU sessionidentifier, and may also include location information of the terminal.The SMF network element may determine to reselect a UPF for the firstPDU session, for example, based on the location information of theterminal. In this case, the SMF network element determines PDU sessionstatus information such as an indication that a current PDU session isnot available. A specific form is not limited.

Step 1607: The SMF network element sends an N11 message to the AMFnetwork element, where the N11 message includes data transmissionchannel information on a core network side, so as to establish a datatransmission channel to a RAN side.

Step 1608: The AMF network element sends an N2 request message to a RANnetwork element, where the message includes NAS service request acceptinformation, and the information may include the PDU session statusinformation, or may optionally include information such as anapplication identifier.

Step 1609: The RAN network element sends an RRC connectionreconfiguration process to the terminal, and in this process, a RANnetwork element side may notify the terminal of the PDU session statusinformation. Optionally, the RAN network element may further notify theterminal of the application identifier information.

Step 1610: After the terminal receives the session status information,the terminal may initiate, based on an indication of the session statusinformation, a new process of establishing a second PDU session. Aspecific form of the PDU session status information is not limited, andmay be that the PDU session is not available, the PDU session isestablished again, or the like.

In the process of establishing the second PDU session, a network sidemay reselect a UPF network element different from the UPF networkelement of the first PDU session for the terminal, to establish thesecond PDU session. In this case, after establishment of the second PDUsession is completed, the terminal establishes, based on the receivedapplication information, a connection to an application indicated by theapplication information, so that a service can be normally performed,and user experience can be improved.

Based on a same technical concept, an embodiment of this applicationfurther provides a mobility management processing apparatus.

FIG. 17 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 401 to step 403 in the procedure shown inFIG. 4, and content related to step 401 to step 403.

Referring to FIG. 17, the apparatus 1700 includes:

a transceiver unit 1701, configured to: receive a data notificationmessage that includes a protocol data unit PDU session identifier andthat is sent by a user plane function UPF network element, anddetermine, based on the PDU session identifier, a session and servicecontinuity SSC mode corresponding to the PDU session identifier and/or aservice area of the user plane function UPF network element, where theUPF network element is a network element that establishes a PDU sessioncorresponding to the PDU session identifier; and

a processing unit 1702, configured to determine a paging area based onthe SSC mode and/or the service area of the UPF network element, where

the transceiver unit is configured to send a first message including thepaging area to an access and mobility management function AMF networkelement, where the first message is used to trigger the AMF networkelement to page, in the paging area, a terminal that establishes the PDUsession by using the UPF network element.

Optionally, the processing unit 1702 is specifically configured to:

if it is determined that the SSC mode is an SSC mode 2, use the servicearea as the paging area; or

if it is determined that the SSC mode is an SSC mode 1 or an SSC mode 3,use, as the paging area, an area indicated by a tracking area list; or

determine the paging area based on the tracking area list and theservice area of the UPF network element.

Optionally, the processing unit 1702 is specifically configured to:

determine, as the paging area, an overlapping area of the service areaand the area indicated by the tracking area list.

Optionally, the first message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times indicatesa quantity of times for which the AMF network element pages theterminal;

a paging cycle, where the paging cycle indicates a cycle in which theAMF network element pages the terminal; and

paging indication information, where the paging indication informationindicates a manner in which the AMF network element pages the terminal.

Optionally, the processing unit 1702 is further configured to:

start a first timer; and

if it is determined after the first timer times out that the AMF networkelement receives no paging response, send packet discard indicationinformation to the UPF network element by using the processing unit,where the packet discard indication information is used to instruct theUPF network element to discard downlink data received from the terminal.

FIG. 18 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 404 and step 405 in the procedure shown inFIG. 4, and content related to step 404 and step 405.

Referring to FIG. 18, the apparatus 1800 includes:

a transceiver unit 1801, configured to receive a first message thatincludes a paging area and that is sent by a session management functionSMF network element, where the paging area is determined by the SMFnetwork element based on a session and service continuity SSC modeand/or a service area of a user plane function UPF network element, theSSC mode and/or the service area of the UPF network element are/isdetermined by the SMF network element based on an obtained protocol dataunit PDU session identifier, and the UPF network element is a networkelement that establishes a PDU session corresponding to the PDU sessionidentifier; and

a processing unit 1802, configured to page, in the paging area by usingthe transceiver unit, a terminal that establishes, by using the UPFnetwork element, the PDU session corresponding to the PDU sessionidentifier.

Optionally, the transceiver unit 1801 is specifically configured to:

send a second message to a radio access network network element, wherethe second message includes a paging area, and the second message isused to trigger the radio access network network element to page theterminal based on the paging area.

Optionally, the paging area in the second message is used by the radioaccess network network element to determine the paging area in which theradio access network network element pages the terminal.

Optionally, the first message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times is usedto indicate a quantity of times of paging the terminal;

a paging cycle, where the paging cycle is used to indicate a cycle ofpaging the terminal; and

paging indication information, where the paging indication informationis used to indicate a manner of paging the terminal.

FIG. 19 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 701 and step 702 in the procedure shown inFIG. 7, and content related to step 701 and step 702.

Referring to FIG. 19, the apparatus 1900 includes:

a transceiver unit 1901, configured to receive a data notificationmessage that includes a protocol data unit PDU session identifier andthat is sent by a user plane function UPF network element; and

a processing unit 1902, configured to determine, based on the PDUsession identifier, at least one of a session and service continuity SSCmode corresponding to the PDU session identifier and a service area ofthe UPF network element, where the UPF network element is a networkelement that establishes a PDU session corresponding to the PDU sessionidentifier, where

the transceiver unit 1901 is configured to send a first message to anaccess and mobility management function AMF network element, where thefirst message includes at least one of the SSC mode and the servicearea, and the first message is used to trigger the AMF network elementto page a terminal that establishes the PDU session by using the UPFnetwork element.

Optionally, the processing unit 1902 is further configured to:

start a first timer; and

if it is determined after the first timer times out that no pagingresponse is received, discard a downlink data packet received from theterminal.

FIG. 20 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 703 and step 704 in the procedure shown inFIG. 7, and content related to step 703 and step 704.

Referring to FIG. 20, the apparatus 2000 includes:

a transceiver unit 2001, configured to receive a first message sent by asession management function SMF network element, where the first messageincludes at least one of a session and service continuity SSC mode and aservice area of a user plane function UPF network element, the SSC modeand the service area are determined by the SMF network element based onan obtained protocol data unit PDU session identifier, and the servicearea is a service area of the user plane function UPF network elementthat establishes a PDU session corresponding to the PDU sessionidentifier; and

a processing unit 2002, configured to: determine a paging area based onat least one of the SSC mode and the service area, and page, in thepaging area, a terminal that establishes the PDU session by using theUPF network element.

Optionally, the processing unit 2002 is specifically configured to:

if it is determined that the SSC mode is an SSC mode 1, determine, asthe paging area, an area indicated by a tracking area list; or

if it is determined that the SSC mode is an SSC mode 2 or an SSC mode 3,determine the service area as the paging area, or determine anoverlapping area of the service area and a tracking area list as thepaging area.

Optionally, the transceiver unit 2001 is specifically configured to:

send a second message to a radio access network network element, wherethe second message includes a paging area, and the second message isused to trigger the radio access network network element to page theterminal based on the paging area.

Optionally, the second message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times is usedto indicate a quantity of times for which the radio access networknetwork element pages the terminal;

a paging cycle, where the paging cycle is used to indicate a cycle inwhich the radio access network network element pages the terminal; and

paging indication information, where the paging indication informationis used to indicate a manner in which the radio access network networkelement pages the terminal.

FIG. 21 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 401 to step 403 in the procedure shown inFIG. 4, and content related to step 401 to step 403.

Referring to FIG. 21, the apparatus 2100 includes:

a transceiver 2101, configured to: receive a data notification messagethat includes a protocol data unit PDU session identifier and that issent by a user plane function UPF network element, and determine, basedon the PDU session identifier, a session and service continuity SSC modecorresponding to the PDU session identifier and/or a service area of theuser plane function UPF network element, where the UPF network elementis a network element that establishes a PDU session corresponding to thePDU session identifier; and

a processor 2102, configured to determine a paging area based on the SSCmode and/or the service area of the UPF network element, where

the transceiver is configured to send a first message including thepaging area to an access and mobility management function AMF networkelement, where the first message is used to trigger the AMF networkelement to page, in the paging area, a terminal that establishes the PDUsession by using the UPF network element.

The apparatus may further include a power supply 2103 (for example, abattery) that supplies power to components. Optionally, the power supply2103 may be logically connected to the processor 2102 by using a powermanagement system, so as to implement functions such as charging,discharging, and power consumption management by using the powermanagement system.

The apparatus may further include a memory 2104, the memory 2104 may beconfigured to store a software program and a module, and the processor2102 runs the software program and the module that are stored in thememory 2104, to perform function applications and data processing of theapparatus.

Optionally, the processor 2102 is specifically configured to:

if it is determined that the SSC mode is an SSC mode 2, use the servicearea as the paging area; or

if it is determined that the SSC mode is an SSC mode 1 or an SSC mode 3,use, as the paging area, an area indicated by a tracking area list; or

determine the paging area based on the tracking area list and theservice area of the UPF network element.

Optionally, the processor 2102 is specifically configured to:

determine, as the paging area, an overlapping area of the service areaand the area indicated by the tracking area list.

Optionally, the first message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times indicatesa quantity of times for which the AMF network element pages theterminal;

a paging cycle, where the paging cycle indicates a cycle in which theAMF network element pages the terminal; and

paging indication information, where the paging indication informationindicates a manner in which the AMF network element pages the terminal.

Optionally, the processor 2102 is further configured to:

start a first timer; and

if it is determined after the first timer times out that the AMF networkelement receives no paging response, send packet discard indicationinformation to the UPF network element by using the processor, where thepacket discard indication information is used to instruct the UPFnetwork element to discard downlink data received from the terminal.

FIG. 22 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 404 and step 405 in the procedure shown inFIG. 4, and content related to step 404 and step 405.

Referring to FIG. 22, the apparatus 2200 includes:

a transceiver 2201, configured to receive a first message that includesa paging area and that is sent by a session management function SMFnetwork element, where the paging area is determined by the SMF networkelement based on a session and service continuity SSC mode and/or aservice area of a user plane function UPF network element, the SSC modeand/or the service area of the UPF network element are/is determined bythe SMF network element based on an obtained protocol data unit PDUsession identifier, and the UPF network element is a network elementthat establishes a PDU session corresponding to the PDU sessionidentifier; and

a processor 2202, configured to page, in the paging area by using thetransceiver, a terminal that establishes, by using the UPF networkelement, the PDU session corresponding to the PDU session identifier.

The apparatus may further include a power supply 2203 (for example, abattery) that supplies power to components. Optionally, the power supply2203 may be logically connected to the processor 2202 by using a powermanagement system, so as to implement functions such as charging,discharging, and power consumption management by using the powermanagement system.

The apparatus may further include a memory 2204, the memory 2204 may beconfigured to store a software program and a module, and the processor2202 runs the software program and the module that are stored in thememory 2204, to perform function applications and data processing of theapparatus.

Optionally, the transceiver 2201 is specifically configured to:

send a second message to a radio access network network element, wherethe second message includes a paging area, and the second message isused to trigger the radio access network network element to page theterminal based on the paging area.

Optionally, the paging area in the second message is used by the radioaccess network network element to determine the paging area in which theradio access network network element pages the terminal.

Optionally, the first message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times is usedto indicate a quantity of times of paging the terminal;

a paging cycle, where the paging cycle is used to indicate a cycle ofpaging the terminal; and

paging indication information, where the paging indication informationis used to indicate a manner of paging the terminal.

FIG. 23 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 701 and step 702 in the procedure shown inFIG. 7, and content related to step 701 and step 702.

Referring to FIG. 23, the apparatus 2300 includes:

a transceiver 2301, configured to receive a data notification messagethat includes a protocol data unit PDU session identifier and that issent by a user plane function UPF network element; and

a processor 2302, configured to determine, based on the PDU sessionidentifier, at least one of a session and service continuity SSC modecorresponding to the PDU session identifier and a service area of theUPF network element, where the UPF network element is a network elementthat establishes a PDU session corresponding to the PDU sessionidentifier, where

the transceiver 2301 is configured to send a first message to an accessand mobility management function AMF network element, where the firstmessage includes at least one of the SSC mode and the service area, andthe first message is used to trigger the AMF network element to page aterminal that establishes the PDU session by using the UPF networkelement.

The apparatus may further include a power supply 2303 (for example, abattery) that supplies power to components. Optionally, the power supply2303 may be logically connected to the processor 2302 by using a powermanagement system, so as to implement functions such as charging,discharging, and power consumption management by using the powermanagement system.

The apparatus may further include a memory 2304, the memory 2304 may beconfigured to store a software program and a module, and the processor2302 runs the software program and the module that are stored in thememory 2304, to perform function applications and data processing of theapparatus.

Optionally, the processor 2302 is further configured to:

start a first timer; and

if it is determined after the first timer times out that no pagingresponse is received, discard a downlink data packet received from theterminal.

FIG. 24 is a schematic structural diagram of a mobility managementprocessing apparatus according to an embodiment of this application. Theapparatus may perform step 703 and step 704 in the procedure shown inFIG. 7, and content related to step 703 and step 704.

Referring to FIG. 24, the apparatus 2400 includes:

a transceiver 2401, configured to receive a first message sent by asession management function SMF network element, where the first messageincludes at least one of a session and service continuity SSC mode and aservice area of a user plane function UPF network element, the SSC modeand the service area are determined by the SMF network element based onan obtained protocol data unit PDU session identifier, and the servicearea is a service area of the user plane function UPF network elementthat establishes a PDU session corresponding to the PDU sessionidentifier; and

a processor 2402, configured to: determine a paging area based on atleast one of the SSC mode and the service area, and page, in the pagingarea, a terminal that establishes the PDU session by using the UPFnetwork element.

The apparatus may further include a power supply 2403 (for example, abattery) that supplies power to components. Optionally, the power supply2403 may be logically connected to the processor 2402 by using a powermanagement system, so as to implement functions such as charging,discharging, and power consumption management by using the powermanagement system.

The apparatus may further include a memory 2404, the memory 2404 may beconfigured to store a software program and a module, and the processor2402 runs the software program and the module that are stored in thememory 2404, to perform function applications and data processing of theapparatus.

Optionally, the processor 2402 is specifically configured to:

if it is determined that the SSC mode is an SSC mode 1, determine, asthe paging area, an area indicated by a tracking area list; or

if it is determined that the SSC mode is an SSC mode 2 or an SSC mode 3,determine the service area as the paging area, or determine anoverlapping area of the service area and a tracking area list as thepaging area.

Optionally, the transceiver 2401 is specifically configured to:

send a second message to a radio access network network element, wherethe second message includes a paging area, and the second message isused to trigger the radio access network network element to page theterminal based on the paging area.

Optionally, the second message further includes a paging policy; and

the paging policy includes one or more of the following:

a quantity of paging times, where the quantity of paging times is usedto indicate a quantity of times for which the radio access networknetwork element pages the terminal;

a paging cycle, where the paging cycle is used to indicate a cycle inwhich the radio access network network element pages the terminal; and

paging indication information, where the paging indication informationis used to indicate a manner in which the radio access network networkelement pages the terminal.

An embodiment of this application further provides a computer readablestorage medium, configured to store a computer software instruction usedfor performing an operation that needs to be performed by the foregoingprocessor, and the computer software instruction includes a program usedfor performing an operation that needs to be performed by the foregoingprocessor.

A person skilled in the art should understand that the embodiments ofthis application may be provided as a method, a system, or a computerprogram product. Therefore, this application may use a form of hardwareonly embodiments, software only embodiments, or embodiments with acombination of software and hardware. Moreover, this application may usea form of a computer program product that is implemented on one or morecomputer-usable storage media (including but not limited to a magneticdisk memory, an optical memory, and the like) that includecomputer-usable program code.

This application is described with reference to the flowcharts and/orthe block diagrams of the method, the device (system), and the computerprogram product according to this application. It should be understoodthat computer program instructions may be used to implement each processand/or each block in the flowcharts and/or the block diagrams, and acombination of a process and/or a block in the flowcharts and/or theblock diagrams. These computer program instructions may be provided fora general-purpose computer, a dedicated computer, an embedded processor,or a processor of any other programmable data processing device togenerate a machine, so that the instructions executed by a computer or aprocessor of any other programmable data processing device generate anapparatus for implementing a specified function in one or more processesin the flowcharts and/or in one or more blocks in the block diagrams.

These computer program instructions may be stored in a computer readablememory that can instruct the computer or any other programmable dataprocessing device to work in a specific manner, so that the instructionsstored in the computer readable memory generate an artifact thatincludes an instruction apparatus. The instruction apparatus implementsa specified function in one or more processes in the flowcharts and/orin one or more blocks in the block diagrams.

These computer program instructions may also be loaded onto a computeror another programmable data processing device, so that a series ofoperations and steps are performed on the computer or the anotherprogrammable device, thereby generating computer-implemented processing.Therefore, the instructions executed on the computer or the anotherprogrammable device provide steps for implementing a specified functionin one or more processes in the flowcharts and/or in one or more blocksin the block diagrams.

Apparently, a person skilled in the art can make various modificationsand variations to this application without departing from the spirit andscope of this application. This application is intended to cover thesemodifications and variations of this application provided that they fallwithin the scope of protection defined by the following claims and theirequivalent technologies.

What is claimed is:
 1. A session management method, wherein the methodcomprises: obtaining, by a session management network element, locationinformation of a terminal device and a session identifier of a firstsession of the terminal device; determining, by the session managementnetwork element based on the location information of the terminal deviceand the session identifier of the first session, to re-select a userplane network element of the first session; and; triggering, by thesession management network element by using a mobility managementnetwork element, the terminal device to establish a second session. 2.The method according to claim 1, wherein the obtaining, by a sessionmanagement network element, location information of a terminal deviceand a session identifier of a first session of the terminal devicecomprises: when the terminal device initiates a service request process,receiving, by the session management network element, the locationinformation of the terminal device and the session identifier from amobility management network element.
 3. The method according to claim 1,wherein the triggering, by the session management network element byusing a mobility management network element, the terminal device toestablish a second session comprises: instructing, by the sessionmanagement network element, the mobility management network element toinitiate a process of releasing the first session.
 4. The methodaccording to claim 1, wherein the session and service continuity mode ofthe first session is mode
 2. 5. The method according to claim 1, whereina location of the terminal device is not in a service area of the userplane network element of the first session.
 6. The method according toclaim 1, the method further comprising: when a terminal device initiatesa service request process, sending, by a mobility management networkelement, location information of the terminal device and a sessionidentifier of a first session to a session management network element;and receiving, by the mobility management network element, firstinformation from the session management network element, wherein thefirst information is used to trigger the terminal device to establish asecond session.
 7. The method according to claim 1, wherein the methodfurther comprising: receiving, by the mobility management networkelement, second information from the session management network element,wherein the second information is used to instruct the mobilitymanagement network element to initiate a process of releasing the firstsession.
 8. A session management network element, comprising: anon-transitory memory and at least one processor coupled to the memory,wherein the at least one processor is configured to execute instructionsstored in the memory to cause the apparatus to: obtain locationinformation of a terminal device and a session identifier of a firstsession of the terminal device; determine based on the locationinformation of the terminal device and the session identifier of thefirst session, to re-select a user plane network element of the firstsession; and; trigger by using a mobility management network element,the terminal device to establish a second session.
 9. The sessionmanagement network element according to claim 8, wherein the at leastone processor is configured to execute instructions stored in the memoryto cause the apparatus to: when the terminal device initiates a servicerequest process, receive the location information of the terminal deviceand the session identifier from a mobility management network element.10. The session management network element according to claim 8, the atleast one processor is configured to execute instructions stored in thememory to cause the apparatus to: instruct the mobility managementnetwork element to initiate a process of releasing the first session.11. The session management network element according to claim 8, whereinthe session and service continuity mode of the first session is mode 2.12. The session management network element according to claim 8, whereina location of the terminal device is not in a service area of the userplane network element of the first session.
 13. A system comprising: amobility management network element; and a session management networkelement, the session management network element being configured toobtain location information of a terminal device and a sessionidentifier of a first session of the terminal device; determine based onthe location information of the terminal device and the sessionidentifier of the first session, to re-select a user plane networkelement of the first session; and; trigger by using a mobilitymanagement network element, the terminal device to establish a secondsession
 14. The system according to claim 13, wherein the sessionmanagement network element is configured to: when the terminal deviceinitiates a service request process, receive the location information ofthe terminal device and the session identifier from a mobilitymanagement network element.
 15. The system according to claim 13,wherein the session management network element is configured to:instruct the mobility management network element to initiate a processof releasing the first session.
 16. The system according to claim 13,wherein the session and service continuity mode of the first session ismode
 2. 17. The system according to claim 13, wherein a location of theterminal device is not in a service area of the user plane networkelement of the first session.
 18. The system according to claim 13,wherein the mobility management network element is configured to: when aterminal device initiates a service request process, send locationinformation of the terminal device and a session identifier of a firstsession to a session management network element; and receive firstinformation from the session management network element, wherein thefirst information is used to trigger the terminal device to establish asecond session.
 19. The system according to claim 13, wherein themobility management network element is configured to: receive, secondinformation from the session management network element, wherein thesecond information is used to instruct the mobility management networkelement to initiate a process of releasing the first session.